This invention is directed to a selectable rate syringe pump for the delivery of insulin or other similar medication, including selection of the interval between motor-driven syringe advance and including control of the plunger displacement for delivery of an insulin bolus of predetermined size.
This pump is in the field of slow-rate, highly accurate dispensing pumps which can be used to inject small amounts of medication at a relatively constant rate for days at a time. This pump is sufficiently small that it can be carried on the patient's body. Such pumps have been found to be useful in treating certain diseases, such as cancer, where a slow, continuous infusion of medication seems to produce good results.
Another medical field of use is in the treatment of diabetes where a slow suitable rate of insulin dispensing provides for the patient's basal physiological requirements. A constant flow of insulin can be substituted by small, discrete amounts of medication at periodic intervals. Since the medication is subcutaneously administered, the diffusion of medication through the tissues provides a substantially steady supply to the physiological system. The regular dispensing of small amounts at relatively short periodic intervals does not appreciably differ from a constant rate injection.
In the field of diabetes, it has been found that most patients need approximately 0.014 unit of insulin per hour per kilogram of body weight. In addition, the patient needs an additional amount or "bolus" for each meal so that the food ingested can be properly metabolized. The amount of insulin in such a bolus usually depends on the amount and type of food to be eaten and the patient's own metabolic requirements. It is, therefore, desirable to have a pump which dispenses insulin at a substantially continuous rate and to have an additional capability for dispensing a bolus of predetermined size at a selected time.
The variable rate syringe pump of this invention is, in its preferred embodiment, particularly arranged for the delivery of insulin, and the invention is described as an insulin delivery system throughout this specification. However, it is clear that it is useful for the delivery of other medications to the body. For example, Heparin can be usefully delivered by this system. Furthermore, chemotherapy medication can be administered and controlled by the variable rate syringe pump of this invention. Thus, any medication which is desirably delivered to the patient over a prolonged period can be properly administered by the variable rate syringe pump of this invention. Liquid nourishment (hyperalimentation) can also be delivered.
Physicians have found that, when insulin is delivered to the body of the patient in very small doses regularly around the clock, the medical effect is better than if the medication is injected in infrequent large doses, such as by manual injection which is the orthodox method by which diabetics take insulin. As a result, a number of devices have been designed which are intended to administer medication at a "constant" rate. Injection systems in the prior art include M. Frey, et al., U.S. Pat. No. 3,395,704 which teaches a simple motor-operated syringe. D. Whitney, et al., U.S. Pat. Nos. 4,269,185 and 4,273,122 teach motor-operated syringes wherein the delivery rate is selected. W. Jewett, U.S. Pat. No. 3,415,419 has a rate selection system for the drive of a motor which actuates a syringe or a roller pump. A. Ruegg, U.S. Pat. No. 4,157,716 describes a syringe which is power-driven and in which the drive is stopped when a predetermined volume of medication has been dispensed. Such constant rate or constant volume delivery devices are useful in various medication-dispensing applications. However, when employed with the delivery of insulin, some of them require the dilution of standard insulin medication. Furthermore, in the treatment of diabetes, it is desirable to have a "base" rate dispensing which is related to the patient's general metabolism and to also have provision for the dispensing of a bolus of predetermined medication volume, on demand, such as at mealtimes.
Other pumps of the syringe type usually have one base rate of delivery or a very narrow range. The basal requirements are met by diluting the standard 100 units/cubic centimeter insulin medication so that, at the rate of delivery of the particular pump, the patient will receive the proper number of insulin units per hour, in accordance with his physiological demand. Dilution of the insulin is tedious and is subject to error. Dilution is required in these systems because the base rate of the pump is difficult to change after the pump is filled with the diluted insulin. The Mill-Hill pump is available from Harvard Apparatus, So. Natick, Mass. and is of a type where a bolus can be delivered by manually turning a knob to advance the plunger of the syringe. The advance of the plunger dispenses the insulin, but such an advance is cumbersome and prone to mistakes. Furthermore, it is not preselectable as to size. The Auto-Syringe pump produced in Hooksett, N.H., delivers a bolus upon operator command. The operator presses a fast-rate delivery switch and delivery continues until the operator releases the fast-rate delivery switch. He can observe delivery by way of a display unit which shows the number of units which have been delivered. This requires the operator's full attention and full time during the bolus delivery. In addition, this pump requires insulin dilution for base rate medication control.
The system described in George G. Siposs U.S. Pat. No. 4,398,908 for "Insulin Delivery System," Ser. No. 210,780. filed Nov. 28, 1980, provides for U-100 insulin being used, variable base rates and preselectable bolus size but the bi-valve reciprocating pump system is prone to air-lock between the valves.